Thermodynamic and Kinetic Study of Cleavage of the N鈥揙 Bond of N-Oxides by a Vanadium(III) Complex: Enhanced Oxygen Atom Transfer Reaction Rates for Adducts of Nitrous Oxide and Mesityl Nitrile Oxide

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• 作者：Taryn D. Palluccio ; Elena V. Rybak-Akimova ; Subhojit Majumdar ; Xiaochen Cai ; Megan Chui ; Manuel Temprado ; Jared S. Silvia ; Anthony F. Cozzolino ; Daniel Tofan ; Alexandra Velian ; Christopher C. Cummins ; Burjor Captain ; Carl D. Hoff
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：July 31, 2013
• 年：2013
• 卷：135
• 期：30
• 页码：11357-11372
• 全文大小：753K
• 年卷期：v.135,no.30(July 31, 2013)
• ISSN：1520-5126

文摘

Thermodynamic, kinetic, and computational studies are reported for oxygen atom transfer (OAT) to the complex V(N[t-Bu]Ar)₃ (Ar = 3,5-C₆H₃Me₂, 1) from compounds containing N鈥揙 bonds with a range of BDEs spanning nearly 100 kcal mol^鈥?: PhNO (108) > SIPr/MesCNO (75) > PyO (63) > IPr/N₂O (62) > MesCNO (53) > N₂O (40) > dbabhNO (10) (Mes = mesityl; SIPr = 1,3-bis(diisopropyl)phenylimidazolin-2-ylidene; Py = pyridine; IPr = 1,3-bis(diisopropyl)phenylimidazol-2-ylidene; dbabh = 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene). Stopped flow kinetic studies of the OAT reactions show a range of kinetic behavior influenced by both the mode and strength of coordination of the O donor and its ease of atom transfer. Four categories of kinetic behavior are observed depending upon the magnitudes of the rate constants involved: (I) dinuclear OAT following an overall third order rate law (N₂O); (II) formation of stable oxidant-bound complexes followed by OAT in a separate step (PyO and PhNO); (III) transient formation and decay of metastable oxidant-bound intermediates on the same time scale as OAT (SIPr/MesCNO and IPr/N₂O); (IV) steady-state kinetics in which no detectable intermediates are observed (dbabhNO and MesCNO). Thermochemical studies of OAT to 1 show that the V鈥揙 bond in O鈮(N[t-Bu]Ar)₃ is strong (BDE = 154 卤 3 kcal mol^鈥?) compared with all the N鈥揙 bonds cleaved. In contrast, measurement of the N鈥揙 bond in dbabhNO show it to be especially weak (BDE = 10 卤 3 kcal mol^鈥?) and that dissociation of dbabhNO to anthracene, N₂, and a ³O atom is thermodynamically favorable at room temperature. Comparison of the OAT of adducts of N₂O and MesCNO to the bulky complex 1 show a faster rate than in the case of free N₂O or MesCNO despite increased steric hindrance of the adducts.